This invention relates to catalytic converters including a housing through which gases are passed and a loose catalyst material contained in the housing and contacted by the gases. The invention may find particular application in converters which, by virtue of catalytic combustion, recombine waste gases obtained during the operation of nuclear power plants. The waste gases obtained during the operation of nuclear power plants contain mostly (approximately 90.degree.) oxygen and hydrogen (radiolysis gases).
The entire quantity of waste gases, prior to its release into the atmosphere, has to be introduced to a processing plant for removing or delaying the radioactive matter it contains. Since the dimensions of this plant depend upon the quantity of the waste gases, it is a desideratum to decrease the waste gas quantities prior to their processing. For this purpose, the waste gases are passed through a converter in which the radiolysis gases are submitted to a catalytic combusion and are thus converted to water.
Such a converter -- hereinafter referred to as a "recombiner" - usually comprises a housing with a lateral or central gas inlet nipple and a usually centrally arranged outlet nipple. In the housing, there is situated a grid-like intermediate floor (screen) which supports a loose catalyst mass constituted of small spheres or cylinders having a diameter of approximately 3 - 8 millimeters. The waste gases obtained during the operation of the nuclear power plant are generally drawn from the turbine condenser by means of vapor jet pumps. Subsequently, the waste gases are introduced, together with the carrier vapor, into the recombiner by first passing them through a dehydrator and preheater. The vapor-gas mixture introduced into the recombiner housing through the inlet nipple first encounters an inlet skirt which deflects the mixture stream into the upper free space of the housing. Then the mixture stream, deflected by the inner face of the housing top, proceeds downwardly and contacts the catalyst. It has been found that during the operation of such a system, unfavorable conditions arise as the flow is formed in the upper housing portion. Under certain flow velocities, the stream, which laterally impinges upon the catalysts, sets the catalyst particles in motion and thus shifts the loose catalyst mass, whereby hills and valleys are formed therein. These, because of the thus obtained different throughflow resistances of the catalyst mass, cause a non-uniform contacting between the vapor-gas mixture and the catalysts. Further, the above-noted motion of the loose catalyst material causes an abrasion thereof and thus reduces the quantity of the catalyst particles and increases pressure losses due to dust deposits. Also, the catalyst bodies tend to be destroyed as the incoming vapor-gas mixture carries them away and hurls them against the housing wall. All these phenomena have an unfavorable effect on the efficiency of the recombiner.